1. Field of the Invention
This invention relates to a method for the manufacture of thermoset plastic articles from a fiber reinforced molding compound.
2. Background Prior Art
Polyester resinous compositions; i.e., ethylenically unsaturated polyester oligomers dissolved in a reactive diluent in the form of a vinyl monomer crosslinking agent, typically styrene, enjoy widespread recognition in the industry as the resin of choice for use in a variety of laminating and bulk molding applications. The latter application accounts for the major usage of such resin compositions. These moldings for the most part are prepared by a compression molding operation in which the moldable charge exists in the form of a fiber reinforced molding compound. Perhaps the most utilized of such molding compounds is the sheet molding compound which in the trade is customarily referred to as SMC. As the name implies SMC consists of an extended length of the molding compound which can vary in thickness and width, typically of such dimensions being in the order of 1/4" and 24", respectively. Besides reinforcement, the SMC can contain a filler and pigment as well as the usual adjuvant amounts of a free radical polymerization initiator, promoter, inhibitor, mold release agent, etc. Due to the incorporation of an ionic bonding thickener in the form of an alkaline earth metal oxide or hydroxide, the SMC physically exists as a relatively non-tacky leathery material which handles conveniently in appropriately sizing a desired mold charge. The use of the prior art SMC, however, poses a problem in that the odor of styrene is unpleasant and becomes extremely aggravatingly so at the elevated temperatures experienced in the molding operation. The practice of the present invention on the other hand completely obviates this particular shortcoming of the prior art.